1. Field of the Invention
The present invention relates to a fluorescence spectrophotometer for measuring fluorescence emitted from a sample by means of irradiating the sample with lights of a specific wavelength as excitation lights.
2. Description of Related Art
Fluorescence spectrophotometer is a device for performing relevant qualitative and quantitative analysis on a sample by allowing the substance to absorb lights (excitation lights) to have an excitation state and measuring the lights (fluorescence) emitted during the process of recovering from the excitation state to a ground state. The fluorescence spectrophotometer has the advantageous effects in terms of sensitivity and accuracy of quantitative measurement and can also be used as a detector for liquid chromatography.
Referring to FIG. 5, a common fluorescence spectrophotometer is illustrated. After the lights emitted from a light source 31 are split by a first splitting portion, that is, a light splitting portion at an excitation side (a diffraction grating 32, a slit 33), a light of an expected wavelength (excitation light) is irradiated to the sample in the sample element 35. The light irradiated onto the sample excites a part of electrons in the sample molecules having energy corresponding to the light, such that the sample molecules are caused to have an excitation state. Then, after the lights emitted during the process of recovering from the excitation state to the ground state are split by a second splitting portion, that is, the light splitting portion at the fluorescence side (a diffraction grating 36, a slit 37), the lights serve as lights of an expected wavelength λEm for the sample fluorescence to reach an detecting portion 38. The fluorescence intensity is determined depending upon the intensity of the excitation light, such that the measurement on the fluorescence intensity may be significantly affected by the fluctuation of the excitation light intensity. In order to compensate the fluctuation of the excitation light intensity, the excitation light λEx from the light splitting portion at the excitation light side is split by a beam splitter 34 before being incident to the sample element 35, and a part of the lights is guided into a reference light detecting portion 39 as a reference light λR. After the signals from the fluorescence detecting portion 38 and the reference light detecting portion 39 are transmitted to a calculating portion 40, the output of the fluorescence detecting portion is calculated. The influences due to the fluctuation of the excitation light are restricted by taking the ratio of the fluorescence intensity to the intensity of the excitation light as the output of the fluorescence detecting portion. As disclosed in Japan Publication No. S63-88412, Japan Publication No. H03-274427 and Japan Publication No. 2001-83093, the configuration for the split lights to be incident to the sample element 35 is commonly used.